Composite inflatable downhole packer or bridge plug

ABSTRACT

Inflatable packer assemblies and bridge plugs that incorporate selective components made of a composite material, thereby providing improvements in weight, drillability and corrosion resistance. A through-tubing packer assembly is described having end sleeves fashioned partially from composite material of high strength fiber and polymer resin. The inflatable packer element has longitudinal ribs fashioned from composite material with a specialized cross-section having a larger cross-section of rib material in locations where additional bending resistance is required and permits additional elastomeric material to be placed about the ribs in sealing areas. An external casing packer is also described having a composite valve assembly and central mandrel formed primarily of composite material. The mandrel includes metallic fittings for threaded attachments to be made.

[0001] This application claims the priority of U.S. Provisional patentapplication Ser. No. 60/444,439 filed Feb. 3, 2003.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates generally to earth boring and deep wellcompletion tools and methods. In certain aspects, the invention relatesto fabrication materials and methods for constructing inflatable packersor bridge plugs.

[0004] 2. Description of the Related Art

[0005] A subterranean well annulus is that generally annular spacewithin a wellbore between the inside bore wall or casing and the outersurfaces of a pipe or tube that is suspended within the wellbore.Packers and bridge plugs are well tools that are commonly used tosegregate axially adjacent sections of the well annulus to prevent thetransfer of fluids, liquid or gas, from flowing or migrating from oneearth strata to another. Briefly, the packer is a structural barrieralong a short length of the annulus performing the function of erectinga fluid-tight seal at both outer and inner surface perimeters therebypreventing fluid and pressure transfer between axially adjacent wellsections. Through-tubing packers and bridge plugs are also known. Thesedevices are disposed within the interior of a string of productiontubing or the like, and then set within to provide fluid tight sealingtherewithin.

[0006] There are numerous mechanisms available to the driller orhydrocarbon producer for erecting a barrier in the form of a packer. Oneof the several mechanisms is an inflatable packer. Characteristically,inflatable packers comprise an elastomeric boot element around the outerperimeter of a tubular mandrel. Opposite ends of the elastomeric bootare secured to the mandrel. Further, the ends are overlaid by a sleevestructure that is either assembled with or integral with pipe jointstructure. The well annulus, or, alternatively, the tubing interior, isobstructed by expansion of the elastomeric boot from the mandrel. Apressurized charge of fluid is expressed from the mandrel flow borethrough a valve conduit in the mandrel wall or collar. This expressedfluid is channeled between the sleeve underside and the mandrel outersurface thereby expanding the elastomeric boot against the surroundingwell bore or tubing wall.

[0007] When the packer is inflated to expand the elastomeric bootagainst the inside casing, tubing, or borehole wall, extremely high hoopstress is imposed upon the sleeve. Where the packer confineshigh-pressure differentials, the hoop stress is even greater.Accordingly, the packer end sleeve is usually fabricated with highstrength materials. Unfortunately, many high strength metals areadversely affected by the fluids and gases typically present in a wellenvironment: for example, CO₂, H₂ S and production stimulation acids.Additionally, the use of high strength materials for packer componentsmakes it more difficult to drill out the packer assembly should itbecome stuck in the wellbore and have to be removed in that manner.

[0008] Packer service conditions, therefore, strongly dictatefabrication material selection in many instances. More exotic materials,such as high-strength Inconel, have traditionally been used forconstruction of packers to be used in severe condition applications.However, the resulting cost is expensive.

[0009] U.S. Pat. No. 6,269,878, issued to Wyatt et al. relates to thedesign of an inflatable packer assembly. Wyatt explains that any pieceof the packer assembly may be made of “drillable” material, such asfiberglass, drillable plastic, cast iron, aluminum, aluminum alloys,fiber reinforced resin materials and so forth so that the packerassembly may be drilled or milled out of the wellbore. Beyond thisgeneral indication, however, there are no specific suggestions as towhich packer components should be constructed of drillable materials andwhich should not. There is also no indication as to which materials outof the list provided are best used for particular components.

[0010] Accordingly, it is an object of the present invention to providea packer construction from materials that are sufficiently strong formost applications and yet are substantially impervious to the chemistryof most downhole fluids. It is also an object of the present inventionto provide a packer device that is both strong and relatively inert tocorrosive well fluids. An additional object of the invention is toprovide a packer sleeve construction that is substantially comprised ofhigh strength composite materials such as carbon or aramid fiber boundin a polymer composition. A further object of this invention is toprovide a packer construction having improved packer performance andlife.

SUMMARY OF THE INVENTION

[0011] Packer assemblies are described that incorporate selectivecomponents made of a composite material, thereby providing improvementsin weight, drillability, corrosion resistance, and overall packerperformance. In one described embodiment, a through-tubing packerassembly is described having end sleeves that are fashioned partiallyfrom composite material.

[0012] A packer end sleeve construction is described that utilizes acomposite of high strength fiber and polymer resin. The fibers areformed of high strength aramid or carbon, so that the resultingcomposite of fiber and resin will have tensile strengths approaching 300ksi. In forming the end sleeve, the fibers are wrapped in layers andoriented in a manner to address particular expected stress conditions.If high hoop stresses will be imposed upon a particular component, thefibers within the composite material will be primarily oriented in acircumferential direction for maximum hoop strength. If axial strainwill be imposed upon the component, a portion of the fibers will beoriented in position that is substantially normal to the circumferencein order to increase axial strength. The fibers are bound in a hightemperature thermoplastic matrix, such as PEEK(poly-ether-ether-keytone).

[0013] Additionally, the inflatable packer element is surrounded by aplurality of longitudinal ribs that are fashioned from compositematerial. The ribs have a specialized cross-section that provides for alarger cross-section of rib material in locations where additionalbending resistance is required and a smaller cross-section of ribmaterial where such bending resistance is not required. The rib designpermits additional elastomeric material to be placed about the ribs insealing areas. The ribs are constructed of several plys of varyingorientations to address the different stresses encountered throughoutthe length of a rib.

[0014] A support sleeve fashioned of KEVLAR® or another suitably strongcomposite material is located at the interface of the expandable bladderand end sleeve in order to provide reinforcement to the compositeportions of the end sleeve against expansive forces. This sleeveconstruction is provided over the rib area of a packer sleeve where amajority of hoop stress is applied. The support sleeve changes theoutward radial stress that is applied to the lower portion of the endsleeve by flattening the geometry of rib deployment during inflation ofthe bladder. Due to the necessity for threaded assembly of the packersleeve to the remaining pipe structure, the composite sleeveconstruction may be hybridized with threaded steel inserts.

[0015] An exemplary external casing packer is also described thatincorporates a central mandrel that is formed primarily of compositematerial. The mandrel also includes metallic fittings for threadedattachments to be made. If desired, the entire external casing packerassembly can be made of composites, including the valve collar. A valvecollar that is fashioned of composite material is more easilymanufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The advantages and further aspects of the invention will bereadily appreciated by those of ordinary skill in the art as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings in which like reference characters designate like or similarelements throughout the several figures of the drawing and wherein:

[0017]FIG. 1 is a side view, partially in cross-section, of an exemplarythrough-tubing bridge plug that incorporates an inflatable packerassembly constructed using composite components in accordance with thepresent invention.

[0018]FIG. 2 is a side view, partially in cross-section, of theinflatable packer element of the bridge plug of FIG. 1, shown apart fromthe other components.

[0019]FIG. 3 is a side, cross-sectional detail of an exemplary endsleeve for use in the packer element shown in FIG. 2.

[0020]FIGS. 4A, 4B, 4C, and 4D illustrate an exemplary process forforming a pair of partially composite end sleeves.

[0021]FIG. 5 illustrates, in side cross-section, the annular end capused with the end sleeve shown in FIG. 3.

[0022]FIG. 6 is an axial cross-section taken along lines 6-6 in FIG. 2illustrating the overlapping arrangement of ribs.

[0023]FIG. 7 is a side cross-sectional view of an alternative end sleevefor use in the through-tubing packer element shown in FIG. 2.

[0024]FIG. 8 is a side cross-sectional view of a further alternative endsleeve for use in the through-tubing packer element shown in FIG. 2.

[0025]FIG. 9 is a cross-sectional view of a portion of an exemplary endsleeve arrangement also illustrating a method of securing composite ribswithin a partially composite end sleeve.

[0026]FIG. 10 is a cross-sectional view of a portion of an alternativeend sleeve arrangement also illustrating a method of securing compositeribs within a metallic end sleeve.

[0027]FIG. 11 is a side cross-sectional view of the exemplary compositerib shown in FIG. 11.

[0028]FIG. 12 is an axial cross-sectional view of an exemplary compositerib taken along lines 12-12 in FIG. 11.

[0029]FIG. 13 is an illustrative diagram depicting the overlappingarrangement of a plurality of ribs upon inflation of the bladder elementof a packer assembly.

[0030]FIG. 14 is a side cross-sectional view of an external casingpacker assembly constructed using composite components in accordancewith the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The present invention is directed to designs for inflatablepacker assemblies and bridge plugs that utilize non-metallic,lightweight, composite materials to form for certain components. Theresulting packer assemblies or bridge plugs are lighter in weight andeasier to drill or mill out of the wellbore than conventional packerassemblies. Additionally, the composite portions of the packer or plugassemblies will be more resistant to corrosive downhole chemicals, suchas CO₂ and H₂S, than conventional packer assemblies. At the same time,the packer or plug assemblies will have the hardness and durabilitynecessary to provide adequate threaded connections to other componentswithin a drill string. A suitable composite material for use in formingthe components described herein is a carbon fiber/PEEK matrix.

[0032] Referring first to FIG. 1, there is shown an exemplarythrough-tubing bridge plug 10 that incorporates an inflatable packerassembly. The bridge plug 10 is typically carried on wireline or coiledtubing, in a manner known in the art, and disposed downwardly throughproduction tubing (not shown). When the plug 10 is lowered to a desiredlocation, the plug 10 is set by inflating the inflatable packer element.The mechanics of such setting and inflation are well known and, thus,will not be described in detail here. The plug 10 includes, at its upperend, a fishing neck portion 12 having a reduced diameter externallatching profile 14 by which a fishing tool (not shown) may be securedfor removal of the plug 10 from the production tubing. Below the fishingneck portion 14 is an upwardly and outwardly directed shoulder 16 whichtransitions to an expanded diameter portion 18. A valve assembly sub 20is located directly below the expanded diameter portion 18. The valveassembly sub 20 houses fluid valving used in inflation of the inflatablepacker assembly of the plug 10. The lower end of the valve assembly sub20 presents an annular ring portion 22 having internal threads 24 andexternal threads 26.

[0033] Conventionally, the fishing neck portion 12 and valve assemblysub 20 have consisted of metallic components that are threadedlyconnected to one another. In the plug 10, however, the fishing neckportion 12 and valve assembly sub 20 are unitarily formed as a singletop sub component fashioned of composite material. The use of compositematerial permits the top sub portion of the plug 10 to be easily drilledor milled away in the event that the plug 10 becomes stuck within theproduction tubing and cannot be removed using a fishing tool. Compositematerial also provides for a plug 10 that is lighter in weight and,therefore, more desirable and easily used in situations where thewellbore is angled or substantially horizontal in orientation.

[0034] Below the unitary top sub, a poppet housing 28 is secured bythreading to the exterior threads 26 and encloses poppet 30 andcompression spring 32. The poppet housing 28 is secured by threading atits lower end to spring housing 34. These components operate in awell-known manner to assist inflation of the bladder element of the plug10. A central mandrel 36 is secured at its upper end to the threadedconnection 24 of the top sub described previously and extendsdownwardly. At its lower end, the mandrel 36 is secured to a bullnose 38by threaded connection 40. The mandrel 36 defines a central bore 42along its axial length. Surrounding the mandrel 36 below the springhousing 34 is an inflatable packer element 44, the details of which willbe described in detail shortly. The lower end of the inflatable packerelement 44 is secured by threading to a bottom sub 46, which is fittedwith a bleed plug 48. The bottom sub 46 also supports a shear ring 50,shear adapter 52 and shear screw 54 that are used for normal operationof the inflatable packer element 44, in a manner that is well understoodby those of skill in the art, if removal of the plug 10 is requiredafter setting.

[0035]FIG. 2 illustrates the inflatable packer element 44 of the plug 10apart from the other components of the plug 10 so that its structure andoperation is more easily seen. As best seen there, the packer element 44includes an upper end sleeve 56, packer element portion 58 and lower endsleeve 60. The packer element portion 58 includes a bladder element 62that is fashioned of nitrile rubber, as is known in the art. The bladderelement 62 radially surrounds the central mandrel 36, shown in FIGS. 1and 6. An annular space 63 is schematically illustrated in FIG. 1 asbeing defined between the bladder element 62 and the mandrel 36. As isknown in the art, the bladder element 62 maybe radially inflated to setthe packer element 44 by disposing fluid, under pressure, into theannular space 63, thereby inflating and radially expanding the bladderelement 62. The bladder element 62 is retained within the upper andlower end sleeves 56, 60 by metallic retaining rings 64 and 66 whichseat inside of the end sleeves 56, 60, respectively, thereby trappingthe axial ends of the bladder element 62 between the retaining rings 64,66 and the end sleeves 56, 60.

[0036] Several longitudinal reinforcing ribs 68 are arrangedcircumferentially about the outer surface of the bladder element 62 inan overlapping fashion. The overlapping arrangement of ribs 68 is bestseen by reference to FIG. 6. The ribs 68 are fashioned of compositematerial and will be described in greater detail shortly.

[0037] Referring once again to FIGS. 1 and 2, a pair of enlargedelastomeric sealing elements 70, 72 is shown surrounding the ribs 68.These sealing elements 70, 72 provide contact surfaces that contact andengage the interior of a production tubing string when the bladderelement 62 is inflated. The sealing elements 70, 72 provide for aresilient and fluid tight seal against the interior of the productiontubing. If a larger version of the packer element 44 were to beintegrated into a production tubing string, sealing would occur againstthe casing wall or open hole wall of the well. It is noted that, whilethe sealing elements 70, 72 are illustrated as covering only a portionof the axial length of the ribs 68, the packer element 44 may also beformed so that a sealing element surrounds essentially the entire radialexterior surface of the ribs 68.

[0038] The upper and lower end sleeves 56, 60 are partially comprised ofa composite material and partially comprised of standard metal, such assteel. FIG. 3 depicts an exemplary design for the upper end sleeve 56.It will be understood, however, that the same construction may be usedfor the lower end sleeve 60. As shown, the end sleeve 56 includes afirst, upper portion 74 that is fashioned of metal, typically steel, anda second, lower portion 76 that is fashioned of composite material.Additionally, an annular end cap 78 is secured to the lower end of thesecond portion 74. The annular end cap 78 functions to provide aresilient and strong lower shoulder for the upper end sleeve 56 and,similarly, a resilient and strong upper shoulder for the lower endsleeve 60. The end caps 78also provide optimal resistance to hoop stressforces that are imposed upon the lower end of the upper end sleeve 56and the upper end of the lower end sleeve 60 during inflation of thebladder element 62. It is noted that the first, metallic portion 74 ofthe end sleeve 56 is overlapped by and affixed to the second portion 76over a contact area 80, which is depicted in FIG. 3. The first, upperportion 74 includes a threaded box-type connector 80 that is used toaffix the end sleeve 56 to the spring housing 34.

[0039] In currently preferred embodiments, the composite used to formthe second portion 76 of the end sleeve 56 consists of high strengthfiber and polymer resin. The fibers are preferably formed of aramid(KEVLAR®)or carbon and, when formulated together with the resin, providetensile strengths approaching 300 ksi. As will be described in greaterdetail shortly, a plurality of layers of the fibers are wrappedcircumferentially about the end sleeve 18 for maximum hoop strength andbound in a high temperature thermoplastic matrix. PEEK(poly-ether-ether-keytone) provides a suitable thermoplastic matrix,although other suitable matrixes may be used. An important advantage tothe use of composite material in forming portions of the end sleeves 56,60 is that reinforcing ribs 68 that are formed of a composite materialmay be more easily and securely affixed to the composite portions of theend sleeves 56, 60, as will be described in greater detail shortly, withrespect to FIG. 9.

[0040] The second, lower portion 76 is preferably formed by winding anumber of layers of composite material onto the overlap portion 81 ofthe first, upper portion 74. Referring now to FIGS. 4A, 4B, 4C and 4D,an exemplary, and currently preferred, method of forming a pair ofcomposite end sleeves, such as end sleeves 56 and 60, is illustrated.FIG. 4A is a side cross-sectional view that depicts a pair of metallicend pieces 82, 84 removably disposed upon a tubular section 86 to form aunitary workpiece 88. The metallic end pieces 82, 84 correspond to theupper portion 74 of an end sleeve 56 or 60 as described above. Theexterior radial surface of the overlap portion 81 of each of themetallic end pieces 82, 84 is knurled, grooved or otherwise roughened tohelp the layers of composite material to adhere and become securelyaffixed to the end pieces 82, 84. FIGS. 4B and 4C are external views ofthe workpiece 88 illustrate the application of different layers ofcomposite material. In FIG. 4B, a first layer 90 of composite materialis being wound onto the workpiece 88 as the workpiece 88 is beingrotated about its longitudinal axis 92. The layer is placed onto theworkpiece 88 with an in-situ melting and bonding process without curing.The first layer 90 includes a resin matrix base coating a plurality offiber strands 94 that are oriented generally parallel to one another.The currently preferred composite material layer is formed of highstrength carbon fibers and a PEEK resin matrix. For clarity, only a fewof the strands 94 are depicted in FIG. 4B. However, in practice, thereare numerous such strands within the first layer 90. FIG. 4B illustratesthe winding deposition of the first layer 90 of composite materialwherein the strands 94 are oriented approximately perpendicular to theaxis 92 of the workpiece 88. This fiber orientation allows the firstlayer 90 to provide maximum resistance to hoop stresses that would actradially outwardly upon the second, lower portion 76 of an end sleeve.It is noted that the first layer 90 is deposited circumferentially alongeach of the overlap portions 81 of the end pieces 82, 84 as well as thetubular section 86. FIG. 4C illustrates the deposition of a second layer96 of composite material after the first layer 90 has been fullydeposited onto the workpiece 88. The second layer 96 also includes aresin matrix coating a plurality of substantially parallel fibers 98.However, the second layer 96 is applied so that the fibers 98 areoriented at an angle α that is less than 90 degrees with the axis 92.

[0041] Additional layers are applied to the workpiece 88 until anannular wall of composite material is built up upon the workpiece 88. Itmay be necessary to adjust the amount of deposition upon variousportions of the workpiece 88 in order to provide the annular compositewall (indicated as 100 in FIG. 4D) with an outer surface ofsubstantially uniform diameter. Such adjustments are within the skill ofthose in the art. Additionally, as the layers of composite material arewound and deposited onto the workpiece 88, the winding should be done sothat the fibers of the composite material making up the second portion76 are oriented so as to maximize the resistance to stress and strainforces that are expected to act upon the second portion 76. In acurrently preferred construction, the workpiece 88 is wound with layersof composite material so that approximately ⅔ of the layers have strandsof reinforcing fibers that are oriented approximately in the axialdirection and approximately ⅓ of the layers have strands of reinforcingfibers that are oriented generally in the circumferential direction. Ithas been found that this construction provides for optimum resistance toboth hoop stress and axially induced forces.

[0042]FIG. 4D depicts the completed workpiece 88 after the wall 100 ofdesired thickness of composite material has been deposited. Once thishas occurred and the composite material has adequately set and cured,the workpiece 88 is then cut along an axial centerline 102 (shown inFIG. 4D). The tubular section 86 may be removed or destroyed, therebyleaving two members formed partially of composite material and partiallyof metallic material. An annular end ring 78 may then be secured to thecomposite end of each of the members to result in a pair of end sleeves,such as end sleeves 56, 60 described earlier. The annular end rings 78are preferably formed of a high-strength steel and are currentlypreferred to offer improved resistance to hoop stresses proximate theend of the end sleeves 56, 60 as well as preventing delamination of thecomposite portions of the end sleeves 56, 60.

[0043] Referring now to FIGS. 7 and 8, two alternative constructions foran end sleeve are shown. In the construction depicted in FIG. 7, an endsleeve 56′ features first, upper portion 74′ that is fashioned of metaland a second, lower portion 76′ that is formed of composite material andis approximately one half of the longitudinal length of the end sleeve56′. The lower portion 76′ presents an annular shoulder 104.

[0044]FIG. 8 illustrates an alternative construction for the end sleeve56″ wherein the second portion 76″ makes up the majority of the endsleeve 56″. The first portion 74″ consists of an annular ring containingthreaded connector 80. The first portion ring 74″ is embedded on theinterior wall of the second portion 76″. It is noted that each of theconstructions depicted provide for the threaded connection of end sleeve56, 56,′ or 56″ to be located on the first, or metal, portion of the endsleeve. Because the composite material used to make up the secondportion is excellent in resisting tension forces, but provides weakinterlaminar shear strength, the threaded connection 20 should not beformed into the second portion, i.e., the composite material ispreferably not threaded.

[0045] In the constructions of end sleeves 56′ and 56″, the annularshoulder 104 is formed of composite material rather than metal. In orderto ensure that this construction provides adequate hoop strength andresistance to wear and hoop stress during inflation of the bladderelement 62, a support sleeve is used. The arrangement depicted in FIG.9, illustrates an annular braided KEVLAR® support sleeve 106 being usedin conjunction with the end sleeve 56′ described earlier. The supportsleeve 106 surrounds that ribs 68 proximate the annular shoulder 104.The KEVLAR® support sleeve 106 reduces the radially outward load appliedto the annular shoulder 104 during inflation of the bladder element 62by flattening the geometry of deployment of ribs 68 during expansion ofthe bladder element 62. The use of composite ribs 68, a KEVLAR® supportsleeve 106, and partially composite end sleeve 56′ has the advantage ofbetter resisting wear that results from repeated inflation and deflationof the bladder element 62, as might occur if the bridge plug 10 iscyclically loaded or moved from location to location within a tubingstring.

[0046]FIG. 9 is also illustrative of a method of securely affixing thecomposite ribs 68 to the second, composite portion 76′ of the end sleeve56′. A series of fusion welds are used to create a secure connection. Ata primary weld point, indicated at 108 in FIG. 9, the composite ribs 68are fused together and to the composite portion 76′ of the end sleeve56′. This fusion is accomplished by melting the matrix material withinthe composite material. Additional, secondary fusion points 110 areshown as well. Still referring to FIG. 9, it is noted that,alternatively, the second, composite portion 76′ of the end sleeve 56′might be disposed over and directly secured to the ribs 68 duringfabrication using the rotational winding technique described above withrespect to FIGS. 4A-4C. In this instance, the ribs 68 would be arrangedabout the tubular section 86 and rotated while layers of compositematerial are wound about them. During the fabrication process for theend sleeve 56′, most of the composite layers are wound so that thecarbon fibers embedded within the composite material are orientedprimarily in the radial direction. The circumferential orientation ofthe fibers within the composite material maximizes that hoop strengththat will be provided by the final end sleeve 56′. Because multiplelayers of composite material are used to construct the end sleeve 56′,some layers of composite material may be oriented so that the fiberswithin are oriented at an angle (such as a 45 degree angle) with respectto the longitudinal axis 92 as required to resist expected stressforces. The use of high-strength, carbon fiber-reinforced composite ribs68 eliminates the plastic deformation or yielding found in traditionalsteel ribs. The ribs 68 are important load-bearing components in aninflatable through-tubing packer assembly and bear combined loading inhigh tensile, bending and twisting when the bladder element of theassembly is inflated. Traditional ribs are made of a high-strengthstainless steel and may be stressed to yielding beyond its elastic limitwhen the bladder element is highly inflated to set the assembly. Thisyielding may prevent the packer assembly or bridge plug from beingeffectively released from setting so that it can be removed from thetubing string or reset in another location. The inventors haverecognized that a composite that includes a PEEK matrix reinforced withadvanced high-strength carbon fiber, such as that commercially known as“IM7,” can provide a full elastic deformation that will be recoveredafter releasing the inflation pressure within the bladder element.

[0047]FIG. 10 illustrates a method of securely affixing the compositeribs 68 to a portion of an end sleeve 112 that might be fashioned ofmetal or of composite material. As shown there, the ribs 68 are fusedtogether at their upper ends to an annular composite load-bearing ring114. The composite ring 114 is formed to present an outwardly anddownwardly facing shoulder 116 that contacts and rests upon acomplimentary inwardly and upwardly facing shoulder 118. Duringinflation of the bladder element, tension forces are applied to the ribs68, generally in the direction shown by arrow 120. These forces aretransmitted to the composite ring 114 and, in turn, applied to theshoulder 118 of the end sleeve 112, as indicated by arrow 122, therebyensuring a secure connection of the ribs 68 to the end sleeve 112.

[0048] The composite ribs 68 have a varying cross-section that places agreater number of fibers and less elastomer in those areas that aresubjected to greater tensile stress. Conversely, fewer fibers and agreater amount of elastomer is provided in areas that are used to createsealing contact (i.e., where the sealing elements 70, 72 will belocated). FIG. 11 illustrates a side, or edgewise, view of a singleexemplary composite rib 68, which is shown apart from other componentsof the bridge plug 10. As shown there, the rib 68 includes two oppositeend portions 124, 126 and a central portion 128. A typical rib 68 mightbe about 48 inches in total length. The central portion 128 has athickness that is less than the thickness of the two end portions 124,126. The thickness of the end portions 124, 126 is approximately 0.016inches while the thickness of the central portion 128 is approximately0.011 inches. As noted, the ribs 68 are formed of a composite material.Preferably, a rib 68 is fabricated by cutting it from a sheet ofsuitable composite material. One suitable composite material for thisapplication is a woven lay of fiber and resin matrix of the typedescribed previously.

[0049]FIGS. 11 and 12 also illustrate a currently preferred constructionfor the composite ribs 68 wherein three plys 130, 134, and 138 ofreinforced composite material are laminated onto one another. As seenthere, the first ply 130 extends along the entire length of the rib 68.The inset drawing illustrates that the reinforcing fibers 132 of thefirst ply 130 are oriented generally parallel to the longitudinal axis135 of the rib 68. A second ply 134 has fibers 136 that are oriented atan angle with respect to the axis 135. It is currently preferred thatthe angle of the fibers 136 approach 90 degrees from the axis 135. It ispointed out that the second ply 134 is present on both end portions 124,126 of the rib 68, but it is not present in the central portion 128 ofthe rib 68. The absence of the second ply 134 in the central portion 128results in the central portion 128 being thinner than the end portions124, 126, which are made up of three plys 130, 134, and 138. The thirdply 138 also extends along the entire length of the rib 68 and, as shownin the inset in FIG. 11, has reinforcing fibers 140 that are oriented tolie generally along the axis 135. The fact that the first and third plys130 and 138 both extend along the entire length of the rib 68 and thatboth have reinforcing fibers 132, 140, respectively, that are orientedgenerally along the axis 135 of the rib 68 provides high axial tensilestrength to the rib 68 and structural stability when the rib 68 istwisted or bent in use. Additionally, the advanced thermoplastic resinPEEK can provide a high fracture toughness and excellent downholeenvironmental and heat resistance, which are important to overall packerlife and performance.

[0050] The composite ribs 68 provide improved response and resistance totensile and bending forces, which will be experienced at or around flexpoints. Thus, the ribs 68 are less likely to fail than ribs ofconventional metallic construction. Additionally, the ribs 68 are of aunique cross-sectional design. During inflation of the bladder element62, the thicker end portions 124, 126 of the ribs 68 will receiveradially inward loading by the shoulders 104 of the end sleeves 56, 60.Because there is a greater cross-section of composite material at thisflex point, the rib 68 will be more resistant to failure due to bendingforces. At the same time, the thinner central portion 128 of the ribs 68remains suitably strong in resistance of tensional loading upon the ribs68 while allowing additional elastomeric material, such as that makingup the sealing elements 70, 72, to be placed upon the outside of theribs 68. The increase in elastomeric material permits a more securefluid-tight seal to be formed by the bridge plug 10.

[0051]FIG. 12 is an axial cross-section taken along lines 12-12 of FIG.11 and illustrates that a rib 68 contains a pair of arcuate portions142,144 that extend laterally outwardly from a central point 146. Thearcuate portions 142, 144 are nestable with like arcuate portions (seeFIG. 13) when the bladder element 62 is inflated and expanded radially.FIG. 13 illustrates portions of three exemplary ribs 68 a, 68 b, and 68c that are arranged in an arcuate fashion and may, in fact be consideredan enlarged view of three of the ribs 68 shown arranged in overlappingfashion about the circumference of a circle in FIG. 6, albeit after thebladder element 62 has been inflated and radially enlarged so that theribs 68 are arcuately spread apart from one another about the entirecircumference of that circle. The ribs 68 a, 68 b, and 68 c are shownapart from other components of a packer assembly for clarity. Each ofthe ribs 68 a, 68 b, 68 c has an arcuate portion 142 that is shaped andsized to easily reside within the arcuate portion 144 of a neighboringrib. In this configuration, the ribs 68 may be spread out relativelyuniformly about the circumference of the circle illustrated in FIG. 6,as will be necessary upon inflation of the bladder element 62. It willbe appreciated, then, that the dual arcuate portion construction of theribs 68 is desirable.

[0052] Turning now to FIG. 14, there is shown an exemplary inflatableexternal casing packer (ECP) assembly 200 that includes componentsfashioned from composite materials. ECP assembly 200 is typicallyincorporated within a casing string, in a manner well known in the art,and disposed into and then set within an open and uncased borehole (notshown). The ECP assembly 200 includes a central tubular mandrel 202 thatdefines an axial casing bore 204 therein. In a currently preferredembodiment, the central mandrel 202 includes a tubular mandrel body 206that is fashioned from composite material. It is noted that the tubularmandrel body 206 may be formed from layers of circumferentially woundreinforced composite material, in a manner similar to that describedearlier for the formation of the composite portions of the workpiece 88.

[0053] Following creation of the composite mandrel body 206, externallythreaded metal end pieces 208, 210 are secured to both the upper andlower axial ends of the mandrel body 206. The end pieces 208, 210 arepreferably fabricated in place upon the mandrel body 206, although othersuitable ways of joining such members together may be used.Alternatively, the composite mandrel body 206 might be integrally formedonto the two metal end pieces 208, 210 in the same manner in which thecomposite portions of the workpiece 88 were built up upon the end pieces82, 84.

[0054] Secured to the outer radial surface of the composite mandrel body206 are a pair of metallic rings 212, 214. The metallic rings 212, 214reside within recessed grooves (visible in FIG. 14) within the compositemandrel body 206.

[0055] An inflatable nitrile bladder assembly, shown generally at 216,radially surrounds the central mandrel 202. The bladder assembly 216includes a radially outer elastomeric cover 218 that surrounds aplurality of longitudinal supporting ribs 220. The ribs 220 may beconstructed of a composite material, like ribs 68 described earlier, orthey may be conventional metallic ribs. End sleeves 222 and 224 securethe bladder assembly 216 to the mandrel 202. The end sleeves 222, 224are preferably fashioned of a suitably strong and durable metal, such assteel, and are secured onto the rings 212, 214 of the mandrel 202. Theend sleeves 222, 224 also securely retain the bladder assembly 216.

[0056] Upper and lower collars 226, 228 are secured by threading to theend pieces 208, 210, respectively. The upper collar 226 is also a valvecollar, which is used to selectively express hydraulic fluid into theECP assembly 200 and inflate the bladder assembly 216 and set the ECPassembly 200 within a wellbore. Both the upper and lower collars 226,228 present box-type threaded connectors 230, 232 for securing the ECPassembly 200 within a casing string (not shown). The upper valve collar226 is formed of a fiber-reinforced composite material. The valve collar226 has a generally cylindrical body with both the upper box-typethreaded connector 230 and a lower box-type threaded connector 234 atits lower end. The lower threaded connector 234 is used to securelyaffix the valve collar 226 to the upper end piece 208 of the centralmandrel 202. The valve collar 226 also has a lateral inflate port 236that is located just beneath the upper threaded connector 230 andpositioned to receive fluid from the lateral exterior of the valvecollar 226. The lateral inflate port 236 is interconnected to an axialfluid passage 238 that extends downwardly from the lateral inflate port236 and opens at the lower end 240 of the valve collar 226. When thevalve collar 226 is securely affixed to the end piece 208 of the centralmandrel 202, the axial fluid passage 238 will become aligned with anadjoining fluid passage 242 housed within the end sleeve 222. The valvecollar 226 thus houses a valve assembly wherein the adjoining fluidpassage 242 is hydraulically interconnected with the bladder assembly216 and, as a result, fluid may be selectively expressed into thelateral inflate port 236 under pressure and then transmitted through thefluid passages 238 and 242 to inflate the bladder assembly 216, therebysetting the ECP assembly 200 within an uncased or cased wellbore.

[0057] During operation, the ECP assembly 200 is operated in a mannertypical of inflatable ECP assemblies. However, the construction of thecentral mandrel 202 is highly advantageous. First, the compositematerial is easier to drill or mill away than steel or other metalstypically used to construct a casing mandrel. Thus, the use of compositematerial in the central mandrel 202 ensures that the ECP assembly 200 iseasier to drill or mill out of the borehole should such becomenecessary. The use of metallic end sleeves 208, 210 and rings 212, 214ensures that secure threaded connections between components areprovided. In addition, the composite material renders the centralmandrel 202 substantially inert and, thus, relatively impervious tocorrosion from wellbore fluids including, for example, CO₂ and H₂Sproduction stimulation acids.

[0058] Additionally, the use of composite materials to form the valvecollar 226 is highly advantageous. Valve collars have heretofore beenformed from steel or a similar metal or metal alloy. Because the valvecollar 226 is located at the uppermost end of the ECP assembly 200, itwill ordinarily be the first part of the assembly 200 that isencountered by a drill in the event that the assembly 200 must bedrilled out of the wellbore. Thus, the use of composite material tocreate the valve collar 226 is particularly advantageous. When the valvecollar 226 is fashioned from composite material, it may be much moreeasily drilled away and, as a result, the ECP assembly released from itswellbore setting. The valve collar 226 may be formed by using any of thetechniques previously described to wind layers of fiber-reinforcedcomposite material onto one another to construct a tubular element. Inaddition, the valve collar 226 might be cast as a single component offiber reinforced composite material. The use of composite materials inthe manner described herein may also result in lower manufacture andassembly costs.

[0059] Those of skill in the art will recognize that numerousmodifications and changes may be made to the exemplary designs andembodiments described herein and that the invention is limited only bythe claims that follow and any equivalents thereof.

What is claimed is:
 1. An inflatable packer assembly comprising: acentral mandrel; an inflatable bladder element surrounding the centralmandrel; a longitudinal rib member disposed adjacent the bladderelement; an end sleeve radially surrounding said central mandrel,bladder element and rib member, said end sleeve having a first portioncomprised of composite material and a second metallic portion.
 2. Theinflatable packer assembly of claim 1 wherein the composite material ofthe first portion of the end sleeve comprises high strength fibers andpolymer resin.
 3. The inflatable packer assembly of claim 1 wherein therib member is also comprised of composite material.
 4. The inflatablepacker assembly of claim 1 further comprising a support sleeve disposedbetween the end sleeve and the rib member, the support sleeve acting toreduce hoop stress forces appled to portions of the end sleeve duringinflation of the bladder element.
 5. The inflatable packer assembly ofclaim 4 wherein the support sleeve is formed substantially of KEVLAR®.6. The inflatable packer assembly of claim 1 wherein the rib memberincludes a pair of end portions having a first thickness and a centralportion having a second thickness and wherein the second thickness isless than the first thickness.
 7. The inflatable packer assembly ofclaim 1 wherein there is a plurality of longitudinal rib members thatare disposed circumferentially about the bladder element and whereineach of the rib mmbers is secured to the end sleeve by at least onefusion weld point.
 8. The inflatable packer assembly of claim 1 whereinthere is a plurality of longitudinal rib members that are disposedcircumferentially about the bladder element and wherein each of the ribmembers is securely affixed to an annular load bearing ring thatpresents an engagement shoulder, the engagement shoulder being inload-transmitting contact with a portion of the end sleeve.
 9. Theinflatable packer assembly of claim 1 wherein the composite materialforming the first portion of the end sleeve comprises circumferentiallywrapped layers of high strength fibers in a resin matrix, the layershaving been applied such that the fibers in at least one of said layersare oriented circumferentially.
 10. An inflatable packer assemblycomprising: a central mandrel having: a mandrel body comprised ofcomposite material; and a metallic portion integrally formed within themandrel body; an inflatable bladder element surrounding the centralmandrel; a longitudinal rib member disposed adjacent the bladderelement; and an end sleeve radially surrounding said central mandrel,bladder element and rib member.
 11. The inflatable packer assembly ofclaim 10 wherein the metallic portion comprises a metallic end piecethat is secured to an axial end of the mandrel body.
 12. The inflatablepacker assembly of claim 10 wherein the metallic portion comprises ametallic ring having a radially external surface with threads thereupon,the metallic ring being disposed upon an outer radial surface of themandrel body.
 13. The inflatable packer assembly of claim 12 wherein themetallic ring is disposed within a recessed groove upon the mandrelbody.
 14. The inflatable packer assembly of claim 10 wherein thecomposite material of the mandrel body comprises high strength fiberwithin a resin matrix.
 15. The inflatable packer assembly of claim 14wherein the resin matrix comprises PEEK.
 16. An inflatable packerassembly comprising: an inflatable bladder assembly; and an end sleevelocated at one axial end of the bladder assembly to secure the bladderassembly to a mandrel, wherein the end sleeve comprises: a first portioncomprised of a composite material consisting essentially of highstrength fiber in a resin matrix; and a second, metallic portion. 17.The inflatable packer assembly of claim 16 wherein the resin matrixcomprises PEEK.
 18. The inflatable packer assembly of claim 16 whereinthe inflatable bladder assembly comprises a plurality of longitudinalrib members for reinforcement of the bladder element, at least one ofsaid plurality of longitudinal rib members being substantially formed ofcomposite material.
 19. The inflatable packer assembly of claim 18wherein the rib members further comprise a pair of end portions having afirst thickness and a central portion having a second thickness andwherein the second thickness is less than the first thickness.
 20. Theinflatable packer assembly of claim 16 wherein the composite materialforming the first portion of the end sleeve comprises circumferentiallywrapped layers of high strength fibers in a resin matrix, the layershaving been applied such that the fibers in at least one of said layersare oriented circumferentially.
 21. An inflatable packer assemblycomprising: a central mandrel having a pair of axial ends; an inflatablebladder element surrounding the central mandrel; a valve collar securedto one axial end of the central mandrel, the valve collar beingconstructed of composite material and retaining a valve assembly forselective transmission of fluid to the inflatable bladder element forinflation of the bladder element.
 22. The inflatable packer assembly ofclaim 21 wherein the central mandrel further comprises a generallycylindrical central portion that is formed of composite material. 23.The inflatable packer assembly of claim 22 wherein the compositematerial of the generally cylindrical central portion further comprisesa plurality of circumferentially wound fiber-reinforced layers ofcomposite material.
 24. The inflatable packer assembly of claim 22wherein the central mandrel further comprises a threaded metallic endsleeve secured to at least one axial end.
 25. The inflatable packerassembly of claim 22 wherein the central mandrel further comprises atleast one threaded metallic ring secured upon an outer radial surface ofthe composite central portion.